In March 1993, Xilinx replaced the XC1700 Series PROMS with the XC1700D family. There were a number of changes and improvements in the D family.
The differences were:
1. New wafer manufacturer (TSMC) 2. Improved ESD protection 3. Availability in a greater variety of packages, including SOIC 4. Different programming voltages (therefore different programming algorithms are required) 5. Programmable reset capability added